Oxygen sensors that contain strontium ferrate, barium ferrate, or strontium-barium ferrate are known (U.S. Pat. No. 4,454,494). In these materials, the central iron atoms of the ferrate lattice are replaced by one to seventy atom-percent of an element from the group composed of titanium, cerium, tantalum, or niobium. The chemical stability limit of these materials is at a temperature of 850.degree. C. with an O.sub.2 partial pressure of pO.sub.2 =10.sup.-18 bar, i.e. these materials decompose during prolonged operation in a reducing atmosphere, in a rich exhaust mixture for example.
The transition from p- to n- semiconducting sensor material in the materials of U.S. Pat. No. 4,454,494 takes place at a relatively high O.sub.2 partial pressure (&gt;10.sup.-10 bar). This results in ambiguity of the sensor signal or insufficient signal at a gas change between rich and lean exhaust. In addition, the materials exhibit a clearly different temperature dependence for different O.sub.2 partial pressure ranges.
An oxygen sensor is known (Chem. Abstr. 112 (1990), reference number 126, 210t) whose sensor material consists of an alkaline-earth-doped lanthanum ferrite. However, this sensor material is not used to measure the change in resistance based on the recorded oxygen partial pressure, but the thermo electric force. In these sensor materials, a significant temperature dependence prevails. To compensate for this temperature dependence, additional measures must be adopted, temperature-regulating measures or precise settings of currents and/or voltages for example. This document therefore contains technical prejudice against oxygen sensors that use the resistive properties of the sensor material. The thermo electromotive force is measured instead.